Many electric vehicles and hybrid electric vehicles, such as series, parallel, and parallel-series hybrids, typically include a high voltage bus and a low voltage bus to distribute electrical power. Typically, the high voltage bus transfers energy between components used to drive the vehicle and the low voltage bus transfers energy to various types of vehicle accessories.
The high voltage bus can be electrically coupled to the low voltage bus by a direct current to direct current (DC-DC) converter, allowing energy to be transferred between the buses. A DC-DC converter receives an input DC voltage with a corresponding input DC current from a power supply and generates an output DC voltage with a corresponding output DC current for use by a load. In a DC-DC boost converter, the output DC voltage is greater than the input DC voltage. As such, conservation of power requires that the output DC current is less than the input DC current. Conversely, in a DC-DC buck converter, the output DC voltage is less than the input DC voltage and the output DC current is greater than the input DC current.
Various electrical system components, including those of the DC-DC converter, are designed or sized for a maximum continuous steady-state current that is shared or divided among various accessory loads. Under some transient operating conditions, the combined accessory load may exceed the steady-state operating current. Strategies for accommodating increased transient loading may include load shedding, i.e. temporarily disconnecting one or more accessory loads from the power supply to reduce the total current demand. Alternatively, a larger power supply or an energy storage device such as an ultra-capacitor may be used to accommodate the transient current demands. However, these solutions generally result in added cost, weight, complexity, and/or increased space for packaging.